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Grounding. That's why USB sucks. If you work with precision instrumentation, USB introduces ground loops and forces unpleasant grounding configurations. I've b

by ISL 13y ago

Grounding. That's why USB sucks. If you work with precision instrumentation, USB introduces ground loops and forces unpleasant grounding configurations. I've been looking for a USB 2.0 High-Speed (who came up with these names, where Full Speed is slower than High Speed?) opto-isolator for years. (Corning's new "3.Optical" cabling looks great, once it makes it to market) HN have any pointers? Edit: Looks like 3.Optical cables appeared for sale ten days ago! http://www.corning.com/news_center/news_releases/2014/2014041501.aspx http://www.corning.com/news_center/news_releases/2014/201404... , http://www.eaccu-tech.com/usb-3-0-optical-cables/usb-3-optical-cable-a-plug-to-a-receptacle-10-meter/ http://www.eaccu-tech.com/usb-3-0-optical-cables/usb-3-optic... Hm. They may be "for sale", but availability may be slim.

tlb 13y ago
A USB over twisted-pair extender, like [1] works. They just look like an extra hub to the USB stack. [1] http://www.digikey.com/product-detail/en/B203-101/B203-101-ND/4438264 http://www.digikey.com/product-detail/en/B203-101/B203-101-N...
- ISL 13y ago
  Interesting. Thanks!
- mindslight 13y ago
  I don't see any mention of isolation in that datasheet, nevermind an actual voltage spec. Granted I haven't looked super hard, but any USB isolator I've seen only ever does full speed. I recall seeing one chip from ADI that was meant for high speed USB isolation, but that's the closest I've come.
  - ISL 13y ago
    Ethernet is transformer-isolated [1]. If you just need to break a DC ground loop, a CAT-5 connection will do it. If you look at the Tripp-Lite's installation manual [2], you'll see that the external power supply is connected to the remote unit. [1] http://electronics.stackexchange.com/questions/27756/why-are-ethernet-rj45-sockets-magnetically-coupled http://electronics.stackexchange.com/questions/27756/why-are... [2] http://www.tripplite.com/shared/techdoc/Owners-Manual/933116.pdf http://www.tripplite.com/shared/techdoc/Owners-Manual/933116...
    - mindslight 13y ago
      Yes, but RJ45 and cat5 don't necessarily imply Ethernet.. DC losses on their own would be high enough to warrant that remote power supply.
      - ISL 13y ago
        Agreed. In the absence of a solution like the 30m 3.Optical, we're desperate enough to try it. We have a working solution using daisy-chained repeaters (for distance) landing in a powered hub, but it's hardly elegant. People make nifty USB-->WiFi interconnects too, but the one we tried can't handle full-bandwidth usage of USB 2.0. It was a sad day when the opto-isolating ADI development board arrived and we discovered, to our chagrin, that Full Speed != High Speed. We were so stoked to have finally found it.
        mindslight 13y ago
        Those terms ("high" vs "full") are especially tricky somehow. Perhaps that ADI chip I mentioned was the same one, and they tricked me as well. At least I was just researching to determine how bad I would want an Ethernet port if I got a PC scope. (I determined the answer was "pretty bad") I don't know why bona fide high-speed isolators are not a common thing. Maybe 12Mbit ends up being sufficient for 98% of cases? It seems like the only way is to find a type of product for which they can't cheat, like those optical 3.0 cables or an actual GigE->USB protocol converter. Then again Tripp-Lite is a big name, and you really would want some isolation for a 300ft run. Good luck!
        mindslight 13y ago
        Answering my own question, I ran across an EEVblog post where someone pointed out the problem is the bidirectional data line. OFC that's why you can't just feed them into a GBIC etc. USB 3 has two unidirectional pairs, and so should be easier to isolate. However, don't get your hopes up for those 3.optical cables to do what you'd like either. USB3 actually just implements 480/12/1.5 by having a parallel USB2 bus the whole way. There is no conversion between the two, which also means you can't actually aggregate 480mbit devices with a USB3 hub the way you'd hope. So who knows if Corning has actually created a full implementation or also just punted.
zokier 13y ago
Do you really need USB specifically? Gigabit ethernet has several optical varieties and provides similar bandwidth.

by ISL 13y ago

tlb 13y ago

A USB over twisted-pair extender, like [1] works. They just look like an extra hub to the USB stack. [1] http://www.digikey.com/product-detail/en/B203-101/B203-101-ND/4438264 http://www.digikey.com/product-detail/en/B203-101/B203-101-N...

ISL 13y ago
Interesting. Thanks!
mindslight 13y ago
I don't see any mention of isolation in that datasheet, nevermind an actual voltage spec. Granted I haven't looked super hard, but any USB isolator I've seen only ever does full speed. I recall seeing one chip from ADI that was meant for high speed USB isolation, but that's the closest I've come.
- ISL 13y ago
  Ethernet is transformer-isolated [1]. If you just need to break a DC ground loop, a CAT-5 connection will do it. If you look at the Tripp-Lite's installation manual [2], you'll see that the external power supply is connected to the remote unit. [1] http://electronics.stackexchange.com/questions/27756/why-are-ethernet-rj45-sockets-magnetically-coupled http://electronics.stackexchange.com/questions/27756/why-are... [2] http://www.tripplite.com/shared/techdoc/Owners-Manual/933116.pdf http://www.tripplite.com/shared/techdoc/Owners-Manual/933116...
  - mindslight 13y ago
    Yes, but RJ45 and cat5 don't necessarily imply Ethernet.. DC losses on their own would be high enough to warrant that remote power supply.
    - ISL 13y ago
      Agreed. In the absence of a solution like the 30m 3.Optical, we're desperate enough to try it. We have a working solution using daisy-chained repeaters (for distance) landing in a powered hub, but it's hardly elegant. People make nifty USB-->WiFi interconnects too, but the one we tried can't handle full-bandwidth usage of USB 2.0. It was a sad day when the opto-isolating ADI development board arrived and we discovered, to our chagrin, that Full Speed != High Speed. We were so stoked to have finally found it.
      - mindslight 13y ago
        Those terms ("high" vs "full") are especially tricky somehow. Perhaps that ADI chip I mentioned was the same one, and they tricked me as well. At least I was just researching to determine how bad I would want an Ethernet port if I got a PC scope. (I determined the answer was "pretty bad") I don't know why bona fide high-speed isolators are not a common thing. Maybe 12Mbit ends up being sufficient for 98% of cases? It seems like the only way is to find a type of product for which they can't cheat, like those optical 3.0 cables or an actual GigE->USB protocol converter. Then again Tripp-Lite is a big name, and you really would want some isolation for a 300ft run. Good luck!
        mindslight 13y ago
        Answering my own question, I ran across an EEVblog post where someone pointed out the problem is the bidirectional data line. OFC that's why you can't just feed them into a GBIC etc. USB 3 has two unidirectional pairs, and so should be easier to isolate. However, don't get your hopes up for those 3.optical cables to do what you'd like either. USB3 actually just implements 480/12/1.5 by having a parallel USB2 bus the whole way. There is no conversion between the two, which also means you can't actually aggregate 480mbit devices with a USB3 hub the way you'd hope. So who knows if Corning has actually created a full implementation or also just punted.

zokier 13y ago

Do you really need USB specifically? Gigabit ethernet has several optical varieties and provides similar bandwidth.